/*
 * Copyright 2010-2012 Susanta Tewari. <freecode4susant@users.sourceforge.net>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package bd.org.apache.commons.math.stat.descriptive.moment;

import bd.org.apache.commons.math.exception.MathIllegalStateException;
import bd.org.apache.commons.math.exception.NullArgumentException;
import bd.org.apache.commons.math.exception.util.LocalizedFormats;
import bd.org.apache.commons.math.stat.descriptive.AbstractStorelessUnivariateStatistic;
import bd.org.apache.commons.math.stat.descriptive.StorelessUnivariateStatistic;
import bd.org.apache.commons.math.stat.descriptive.summary.SumOfLogs;
import bd.org.apache.commons.math.util.FastMath;
import bd.org.apache.commons.math.util.MathUtils;

import java.io.Serializable;

/**
 * Returns the <a href="http://www.xycoon.com/geometric_mean.htm">
 * geometric mean </a> of the available values.
 * <p>
 * Uses a {@link SumOfLogs} instance to compute sum of logs and returns
 * <code> exp( 1/n  (sum of logs) ).</code>  Therefore, </p>
 * <ul>
 * <li>If any of values are < 0, the result is <code>NaN.</code></li>
 * <li>If all values are non-negative and less than
 * <code>Double.POSITIVE_INFINITY</code>,  but at least one value is 0, the
 * result is <code>0.</code></li>
 * <li>If both <code>Double.POSITIVE_INFINITY</code> and
 * <code>Double.NEGATIVE_INFINITY</code> are among the values, the result is
 * <code>NaN.</code></li>
 * </ul> </p>
 * <p>
 * <strong>Note that this implementation is not synchronized.</strong> If
 * multiple threads access an instance of this class concurrently, and at least
 * one of the threads invokes the <code>increment()</code> or
 * <code>clear()</code> method, it must be synchronized externally.</p>
 *
 *
 * @version $Id: GeometricMean.java 1244107 2012-02-14 16:17:55Z erans $
 */
public class GeometricMean extends AbstractStorelessUnivariateStatistic implements Serializable {

    /** Serializable version identifier */
    private static final long serialVersionUID = -8178734905303459453L;

    /** Wrapped SumOfLogs instance */
    private StorelessUnivariateStatistic sumOfLogs;

    /**
     * Create a GeometricMean instance
     */
    public GeometricMean() {

        sumOfLogs = new SumOfLogs();
    }

    /**
     * Copy constructor, creates a new {@code GeometricMean} identical
     * to the {@code original}
     *
     * @param original the {@code GeometricMean} instance to copy
     */
    public GeometricMean(GeometricMean original) {

        super();

        copy(original, this);
    }

    /**
     * Create a GeometricMean instance using the given SumOfLogs instance
     * @param sumOfLogs sum of logs instance to use for computation
     */
    public GeometricMean(SumOfLogs sumOfLogs) {

        this.sumOfLogs = sumOfLogs;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public GeometricMean copy() {

        GeometricMean result = new GeometricMean();

        copy(this, result);

        return result;
    }


    /**
     * {@inheritDoc}
     */
    @Override
    public void increment(final double d) {

        sumOfLogs.increment(d);
    }


    /**
     * {@inheritDoc}
     */
    @Override
    public double getResult() {

        if (sumOfLogs.getN() > 0) {
            return FastMath.exp(sumOfLogs.getResult() / sumOfLogs.getN());
        } else {
            return Double.NaN;
        }
    }


    /**
     * {@inheritDoc}
     */
    @Override
    public void clear() {

        sumOfLogs.clear();
    }


    /**
     * Returns the geometric mean of the entries in the specified portion
     * of the input array.
     * <p>
     * See {@link GeometricMean} for details on the computing algorithm.</p>
     * <p>
     * Throws <code>IllegalArgumentException</code> if the array is null.</p>
     *
     * @param values input array containing the values
     * @param begin first array element to include
     * @param length the number of elements to include
     * @return the geometric mean or Double.NaN if length = 0 or
     * any of the values are &lt;= 0.
     */
    @Override
    public double evaluate(final double[] values, final int begin, final int length) {

        return FastMath.exp(sumOfLogs.evaluate(values, begin, length) / length);
    }


    /**
     * {@inheritDoc}
     */
    @Override
    public long getN() {

        return sumOfLogs.getN();
    }


    /**
     * <p>Sets the implementation for the sum of logs.</p>
     * <p>This method must be activated before any data has been added - i.e.,
     * before {@link #increment(double) increment} has been used to add data;
     * otherwise an IllegalStateException will be thrown.</p>
     *
     * @param sumLogImpl the StorelessUnivariateStatistic instance to use
     * for computing the log sum
     */
    public void setSumLogImpl(StorelessUnivariateStatistic sumLogImpl) {

        checkEmpty();

        this.sumOfLogs = sumLogImpl;
    }


    /**
     * Returns the currently configured sum of logs implementation
     *
     * @return the StorelessUnivariateStatistic implementing the log sum
     */
    public StorelessUnivariateStatistic getSumLogImpl() {

        return sumOfLogs;
    }


    /**
     * Copies source to dest.
     * <p>Neither source nor dest can be null.</p>
     *
     * @param source GeometricMean to copy
     * @param dest GeometricMean to copy to
     * @throws NullArgumentException if either source or dest is null
     */
    public static void copy(GeometricMean source, GeometricMean dest) throws NullArgumentException {

        MathUtils.checkNotNull(source);
        MathUtils.checkNotNull(dest);
        dest.setData(source.getDataRef());

        dest.sumOfLogs = source.sumOfLogs.copy();
    }


    /**
     * Throws IllegalStateException if n > 0.
     */
    private void checkEmpty() {

        if (getN() > 0) {

            throw new MathIllegalStateException(
                LocalizedFormats.VALUES_ADDED_BEFORE_CONFIGURING_STATISTIC, getN());
        }
    }
}
